Subgenomic RNAs:: The possible building blocks for modular recombination of Closteroviridae genomes

The Closteroviridae include several plant viruses of considerable economic importance, with unusually large positive-strand genomes of up to 20 kb. Molecular characterization of several of these viruses has now confirmed their coherent and unique position among the elongated plant RNA viruses. Structural comparisons of their genomes suggested a modular composition. The recent finding of multiple species of citrus tristeza virus (CTV) defective-RNAs, which have apparently resulted from the recombination of a subgenomic (sg)RNA, with distant parts from the 5' end of the CTV genome, suggests that Closteroviridae are probably able to utilize sgRNAs and/or their promoter signals as factors for the modular exchange and rearrangement of their genomes. (C) 1997 Academic Press.